The present invention relates to 1-aza-2-silacyclobutane compounds whose nitrogen is substituted by a hydrocarbon group or a hydrocarbon group that contains a heteroatom-containing functional group. The present invention also relates to a method for the preparation of these compounds.
The 1-aza-2-silacyclobutane compounds known to date include 1-aza-2-silacyclobutane compounds in which carbon is bonded to the nitrogen in the 4-membered ring and 1-aza-2-silacyclobutane compounds in which silicon is bonded to this ring nitrogen. N-(1,1-dimethylethyl)-2,2,6-trimethyl-8-phenyl-1-aza-8-silabicyclo[4.2.0]o ctane-8-amine is an example of the former type of compound. This compound contains some very sterically bulky substituents in order to improve the stability of intermediates generated during its synthesis, but this tactic also reduces the reactivity of this azasilacyclobutane. Furthermore, the synthesis of this compound involves the combination of a number of equivalent reactions, and this compound is problematic from an industrial perspective because of the problem of dealing with by-products as well as the number of steps in its production process. Finally, this azasilacyclobutane is very expensive because the starting reagents used in its synthesis cannot be acquired on an industrial basis.
1-Benzyl-2,2,4-triphenyl-3-isopropyl-1-aza-2-silacyclobutane is another 1-aza-2-silacyclobutane in which carbon is bonded at the 1 position. Due to the extensive introduction of bulky substituents for the purpose of precursor stabilization, this 1-aza-2-silacyclobutane has bulky substituents bonded on all the atoms in the 4-membered ring, and this again results in a loss of reactivity. This azasilacyclobutane is also very expensive because the starting compounds for the precursors cannot be acquired on an industrial basis.
With regard to 1-aza-2-silacyclobutanes in which Si is bonded to the nitrogen in the four-membered ring, Japanese Patent Application Laid Open {Kokai or Unexamined} Number Hei 2-235891 [235,891/1990] discloses the following compound ##STR1## where R is a hydrocarbon group or hydrogen atom and R' is a hydrocarbon group, as a point of departure for the facile stereospecific preparation of 2-amino alcohols by desilylation. According to this invention, 2-amino alcohols are synthesized utilizing the facile hydrolyzability of the two Si--N bonds in the above compound and conversion of the Si--C bond into the Si--O bond by oxidation. Because this compound contains two readily hydrolyzable Si--N bonds, it is difficult to orient cleavage to a particular Si--N bond. When this compound is used, for example, as an endblocker for silanol-terminated siloxane, the following two species are produced, thus creating the problem of by-products: ##STR2## Moreover, because the substituent group on the nitrogen has the --SiR'.sub.2 H structure, any functional group introduced in R' is subject to limitations imposed by the behavior of the Si--N bond. For example, even when a group such as the allyl group is introduced as R', this R' substituent will not be retained in the azasilacyclobutane skeleton and thus cannot be effectively utilized as a functional group in practical applications due to the facile cleavability of the Si--N bond by such reactions as hydrolysis.
The present invention introduces novel 1-aza-2-silacyclobutane compounds whose nitrogen is substituted by a hydrocarbon group or heteroatom-containing hydrocarbon group, whose N--Si bond is highly reactive, and which are very effective as silanol endblocking agents and silane coupling agents. The present invention also introduces a method for the preparation of these novel 1-aza-2-silacyclobutanes.
Furthermore, because a wide selection of N-bonded functional groups is possible for the 1-aza-2-silacyclobutane compounds of the present invention, these compounds are very useful as the corresponding silane coupling agents and endblockers for polysiloxanes, for example, as in the case of allyl, phenyl, substituted phenyl, benzyl, substituted benzyl, and so forth.
Finally, the preparative method of the present invention makes possible the direct, high yield, and highly selective production, from the dihydrocarbylsilyl derivatives of secondary allylamines, of 1-aza-2-silacyclobutane compounds having a functional group bonded to the nitrogen through carbon.